(1) Field of the Invention
The present invention relates to a solid state imaging apparatus including an on-chip color filter, and to a method of manufacturing the same.
(2) Description of the Related Art
In recent years, a solid-state imaging apparatus such as a Charge Coupled Device (CCD) has been miniaturized and the number of pixels of the solid-state imaging apparatus has been increased. However, since the conventional solid-state imaging apparatus including an on-chip color filter has a reduced light-receiving size of a photodiode which is a light-receiving sensor unit, a photoelectric conversion characteristic (light sensitivity) which is a main characteristic of the solid-state imaging apparatus is reduced.
For example, the optical size of a solid-state imaging apparatus mounted in a digital still camera is mainly from one-third inch to one-fourth inch, and one-sixth inch and smaller sizes are being examined. Also, the number of pixels is expanding to the range of two million pixels to five million pixels, and five million pixels or more are being examined. Considering the above mentioned reduced light-receiving size and increased number of pixels, it is necessary to establish a technique which prevents the main characteristics of the solid-state imaging apparatus, from being reduced, such as light sensitivity, mixed colors with the neighboring pixels, and line gradation.
FIG. 1 is a cross-section view of a pixel of the solid-state imaging apparatus disclosed in Japanese Laid-Open patent publication No. 2001-249218. According to the above mentioned solid-state imaging apparatus, (i) the first semiconductor well region 2 which is a second conductive type (for example, P-type) is formed on a semiconductor substrate 1 made of a first conductive type (for example, N-type) silicon semiconductor and (ii) an N-type semiconductor region for making each light-receiving sensor unit 3 of matrix arrangement is formed above the first P-type semiconductor well region 2.
Moreover, via a gate insulating film 4, a transfer electrode 5 made of, for example, polysilicon is formed. Then, via an inter-layer insulating film 6 covering the transfer electrode 5, a photo-shielding film 7 made of AL, W and the like is formed above the overall plane except for the aperture of the light-receiving sensor unit 3. After that, the photo-shielding film 7 is covered with a passivation film 8.
Furthermore, a first clear flat film 9, color filter layers 10G and 10B, and a second clear flat film 11 are sequentially formed. Then, an on-chip microlens 12 which condenses incident light into each light-receiving sensor unit 3 is formed above the flat film 11.
The first clear flat film 9 is a film for eliminating difference in level on the foundation so as to form a stable color filter layer. The second clear flat film 11 is a film for flattening the color filter layers 10G and 10B so as to accurately form the on-chip micro lens 12.
The color filter layers 10G and 10B include: (i) a color filter made of complementary colors such as yellow, cyan, magenta and green (solely, or made by laminating yellow and cyan), or (ii) a color filter made of the primary colors such as red, green and blue, and the like.
The conventional color filter layer is formed by (i) a staining method and (ii) a color resisting method which selects and exposes, to light, a photoresist film including stain and dye and executes a developing process so as to form an intended filter.
According to the improved example as disclosed in the above mentioned Japanese Laid-Open patent publication No. 2001-249218, as measures to avoid (i) decrease in light sensitivity, and (ii) mixed colors between the neighboring pixels which are both caused by a diagonal light, it is essential to make the distance from the semiconductor substrate surface to the second clear flat film 11 short, due to the miniaturization. As such means, making the complementary green filter thin is suggested because the complementary green filter formed by laminating cyan and yellow has a high possibility to be the thickest among the color filter layers.
As such example, in a color filter manufacturing method, the color filter film which has the first color component and does not include any photosensitive materials is selectively etched and formed. Thus, for example, in manufacturing a complementary color filter, if a green filter component is formed using the above mentioned one color method, the green filter component can be formed with the similar thin film thickness to the other color filter components. Therefore, the color filter layer can be made thin.
According to the conventional solid-state imaging apparatus, for the reduced pixel size, measures to make the distance from the semiconductor substrate to the second clear flat film 11 short is suggested. And, some effects are expected regarding the vertical incident light falling into the light-receiving sensor unit 3. However, regarding the diagonal light, due to the shapes of the color filter layers 10G and 10B, the diagonal incident light penetrates the neighboring color filter layers, and falls into the light-receiving sensor unit 3. Thus, colors are mixed, and the necessary spectral characteristic can not be obtained. Moreover, depending on the incident angle of the light, the degree of the mixed colors changes, and problems such as line gradation and sensitivity unevenness are yet to be solved.